Telegraph exchange system



Nov. 21, 1933. A LOCKE Er AL 1,936,200

TELEGRAPH EXCHANGE S YSTEM Filed Dec. 4, 1931 4 Sheets-Sheet 2 e/4, flunk; B 5 FIG. 2 T

POLAR/ZED l -iv STAC DIFFERENTIAL FOL AR/ZED nll mu um Illl Illll llfik r ll lllll I [,I'TTFIT I 6,4. LOG/(E lNl/E/VTORSI LANE A TTORNEV NOV. 21, LOCKE r AL 1,936,200

TELEGRAPH EXCHANGE SYSTEM Filed Dec. 4, 1931 4 Sheets-Sheet s EEIE] 8? @EEE [III] "START" s|.ow OPE RATING GALOCKE lNVENTORS C. a LANE.

8) g ATTORNEV Patented Nbv. 21, 1933 K UNlTEl) STATES TELEGRAPH EXCHANGE SYSTEM George A. Locke, Glenwood, and Cuthbert vC. Lane, Little Neck, N; 1 assigno'rs to Bell Tele-- phone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 4, 1931. Serial No. 578,958

10 claims. (01. 17s- 4) This invention relates to a printing telegraph exchange system by means of which connections may be established quickly and efficiently for communication purposes between any two of a 5 plurality of subscribers" telegraph stations, and further by means of which such connections are to remain thus established for more or less ternporary intervals in accordance with the wishes of the subscribers.

This invention relates to a printing telegraph exchange system which can establish connections between any two of a plurality of subscribers and more particularly to such of those systems which can establish. a communication circuit between a calling subscriber and an unattended station circuit. l

It is known in the art that in manual telegraph exchange systems means may be provided Whereby any telegraph station served by the exchange system may obtain connectioirwith any other substation by signaling'tlie operator at a central ofiice' to which the telegraph station is connected. At the central office a special circuit controlled by an unattended startkeyfmay be provided for the operator to start the driving mechanism at an unattended subscribers station for receiving communication from a calling subscriber. G. A. Locke and F. S. Kinkea'd copending application,

0 such an arrangements 1 It is also desirable in such systems to" bring to the attention of the calling subscriber the will inform thecalling subscriber of the identity of the station'to which the connection is established. Accordingly, a primary object of this'invention is to provide a circuit which will transmit from the central cflice to the calling subscriber a check signal which verifies the code-number of the unattended subscribers station; and moreover thesignal may be sent to the calling subscriber in cases where the called station is attended but the calling subscriber wants the identity of the called subscriber verified.

According to the herein described embodiment of the invention, an impulse sender arrange-' ment individual to each subscribers line circuit is provided at the central office together with a plurality of continuously rotatingdistrihutors of the start-stop type. The distributors are common to the impulse sender arrangements and are eel-n1 No. 459,624, filed June 7, 1930, discloses arranged to repeat the signals respectively corresponding to the numerical digits constituting the subscribers station numbers or codes. Each sender arrangement is connected to a line jack circuit in response to a request for a called subscribers line. The operator at the central ofiice by means of a cord circuit plugs into the". jack of the called subscribers line, operates a'spe'cial, or unattended station, key in the cord circuit to thereby operate the sender circuit arrangement 5 of the called subscribers line. The sender circuit of the called subscribers line is connectedby means or" a cross-connecting rack or bus-bar to the distributors repeating the signals correspond-'- ing to the digits of the called subscribers line 70 and these signals are repeated in properorder through a repeater in the cord circuit to the calling subscribers line whereby the calling subscriber is informed that the connection established by the operator is correct. This service is'required only Whenthe called subscribers station is unattended at the time the call is made.

A'feature of this invention is the provision for informing a calling. subscriber, before a message is transmitted to an unattended station, 80.

that the station to which the connection is established is the correct one.

Another feature of this inventionjis the use of rotary stepper switches for insuring the transmission to acalling subscribers station'of a'complete signal'ior each of the digits of the called subscribers station code. I

Another feature resides ,in providing a separate stepper switch for each of the subscribers stations connected to the central ofiice.

Another feature lies in the use of ten cone tinucusly rotating distributors common to all the subscribers stations connected to the central oflice, wherein the signal combinations corresponding to each of the numbers of the subscribers stations are stored so that combinations constituting any called number may be selected will for transmissionto a calling station.

Other objects and features will appear in the subsequent detailed description taken in conjunction with the accompanying drawings. A system to which the present invention may be suitably adapted is disclosed in the copending application of G. A. Locke and F. S. Kinkead, supra. l

' Referring to the drawings:

Fig.1 shows the circuit diagramof a subscribers loop circuit at station A. A similar cir.- cult is provided for eachof the other subscribers loop circuits in the system. The system shown .1

in Fig. 1 includes suitable audible and visible indice-ting apparatus;

Fig. 2 illustrates in diagrammatic form one of the cord circuits at the central office and in schematic form the equipment at the central oilice which is individual to each subscribers line circuit. Only so much of the equipment is shown that is necessary for the satisfactory understanding of the invention. The cord circuit not shown but diagrammatically represented by a block is described in detail in the application of G. A. Locke and F. S. Kinkead, supra;

Fig. 3 shows the storing device which is common to all subscribers station line circuits terminating in the central office, which is adapted to repeat to a calling subscribers line whenever desired, signal combinations representing the number of the called station to which the connection is established;

Fig. 4 shows the circuit in schematic form of a second subscribers station; and

Fig. 5 shows the manner of arranging the sheets of the drawings for a complete understanding of the system herein described.

Apparatus at station A Referring to Fig. 1 which shows the subsubscribers loop circuit at station A, the equipment shown therein. comprises a printing telegraph sending and receiving unit 10A. Unit 10A comprises a printer magnet 109A, a set of sending contacts 101A and a suitable motor MA equipped with a pair of contacts 113A which will open by mechanical means when motor stop signals are sent. External of the printing telegraph set or unit are switch 102A for starting the printer set motor, a stop or break key 103A for stopping the printer set, a ringer or bell 104A whereby the central oiilce may signal the subscribers station, a test key 105A for testing locally the printer sets while the loop circuit is arranged so that the ringer may be operated from the central office, a flash key 166A for signaling the central office and several relays, the functions of which will be hereinafter described.

Apparatus of the Central Oyfice (station C) Figs. 2 and 3 constitute equipment at the central office.

In Fig. 2 the tip TA lead of the loop circuit oi station A terminates in jack 211A, one such jack being provided at the central office for each sub scribers station in the system. Each of these jacks has associated therewith a line lamp 212A and an auxiliary bell 213A so that each subscriber may signal the central station whenever a connection to another subscribers station is desired. A plurality of cord circuits are provided for respectively establishing connections between calling subscriber and called subscriber stations in a manner well known in the ianually operated telephone exchange systems. A cord circuit is shown which terminates in answering plug 21% and a calling plug 2143. Each cord circuit includes a repeater represented diagrammatically by block 216. The repeaters are of the single line repeater type which repeat signals in either direction between two interconnected subsci ser loop circuits. A'detailed disclosure of a repea'e" unit of this type will not be given in this application since it may be had by referring to the application or" Lccke-Kinkead, supra. A key such as 215 shown in repeater 216, is provided for each repeater and serves two purposes, namely, to start the printer motor at the unattended station in the nesasoo same manner as key shown in Fig. 2 of the Locke-Kinkead application, and to operate the answer-back equipment located at the central ofiice and associated with a called subscriber loop circuit. By means of the answer-back equipment a calling subscriber is informed of the number of the called stations to which a connection has been completed by means of a cord circuit. Key 215 is operated only when the connection between a calling and a called subscriber loop circuit has been completed and the called station is unattended at the time. Key 215 provides an ar rangement whereby the calling subscriber is assured that the connection established is'correct. The answer-back equipment provided at the central office for each of the subscribers stations comprises a group of relays and a stepper switch. The equipment shown on the left-hand side of Fig. 2 is associated with subscribers station A and that shown on the right-hand side is associated with subscribers station B shown in Fig. 4. As soon as a subscribers jack is selected to complete a call its associated stepper switch starts operating in reponse to the operation of the key corresponding to key 215 in cord circuit and repeater 216 and as the switch moves through its first four operated positions, that is, positions Nos. 2 to 5, inclusive, four combinations of impulses corresponding to the numerical digits of the called number in their proper sequence are successively repeated from a source of impulses common to all stations, to the printer set of the calling station. The connections of the contacts or" each stepper switch are connected to the common source of impulse combinations through a bus-bar or cross-connecting rack such as those shown at the bottom of Fig. 2.

In Fig. 3 is shown the common source of impulse combinations which comprises thirteen rotary distributors, one for effecting the start the series or operations of the stepper switch associated with the jack into which the calling end of a cord circuit is inserted, one for transmitting the signal combination eiiective in operating the shift to figures mechanism in the printer typer subscribers station is being transmitted to a calling subscribers station;

Apparatus at station B The apparatus for station B is shown in Fig. 4

and is identical with that shown for station A in Fig. 1.

Operation of the system l-laving briefly discussed the various circuit elements involved .in establishing a connection between local subscribers lines, the mannen in which this connection is established will now be described in detail. Referring to Fig. 1, under normal conditions, a circuit may be trace through a bell ringer 124A from the tip side TA oi the loop, over the normally closed contacts of key 1065, condenser 111A, and bell 194A, contact No. 4 of key 105A, back contact of relay 199A to ground 112A. Also, ground is normally connected to the ring side of the loop in a path from ring lead station A, front contact of relay 199A, No. 6 of key 105A, sending contact 101A of the a night alarm bell or operating switch 225A I 2275 in series with bell'2l3A. relay 223A not Rii'throughthe winding of relay IlOA, contact No. 2 of key 105A, one winding or relay '107A,contact 101A of the subscriberls printer set, contact No.

6 of key 105A, back contact of relay 109A to ground 112A. Forthe' purpose of illustration, it is assumed thatflstation A desires to establish a connection to stationB. Start switch 102A is operated which closes a circuit from one side of power supply PA, through the winding of relay 108A to the other side of the power supply, causing relay 108A to operate. ing, locks up through its'lower contact contact of stop key 103A,1T10t01' control contact 113A of the printer. .In operating, relay, 108A closes a path through its upper contact to start the motor for the printer set and also to operate relay 109A through the same circuit.

The operation of relay 109A opens the bell ringer circuit over the tip leadTA of the loop, removes ground from the ring side RA of the loop' and closes the tip and ring leads of the loop through the subscribers station set to operate relay 219A at the central oflice. This last circuit is traced from negative battery 220A at" the w 3 central office, through theright-hand break contact oifrelay 221A, left-hand winding of relay 219A, the tip side of the loop, normally closed contact or" flash key 106A located at subscribers contact printer'set, one winding of relay 107A, contact No. 2 of key 105A, winding of relay 110A, ring side of loop, .outer right-hand armature and back contact of relay 221A, inner left armature and back contact of relay 222A to ground. The operation of relay 219A completes a path to operate relay 222A, from ground on the armature and contact of relay 219A to'battery through the winding of relay 222A. The operation of relay 222A in turn operates relay 223A. This circuit. is traced from ground on the outer left armature 'andfront contact of relay 222A, to the inner right-hand armature and back contact of relay 221A, through the winding of relay 223A, to grounded battery. Incidentally, relay 219Ais kept from releasing when relay 222A operates by the substitution of grounded positive battery 224A on the left inner armature and front contact of relay 222A, for the ground on the left inner armature and back contact of relay 222A. This positive battery is now connected over-the ring side RA of the loop circuit which may be traced back over the tip lead TA of the loop circuit to grounded negative battery 220A as mentioned hereinbefore. 'Belay 223A, in operating, lights lamp 212A in a circuit traceable from grounded battery on the inner right armature and contact of relay 223A'to ground at lamp 212, indicating to the operator at the central office that the subscriber at station A is calling. If desired, the operation'of relay 223 may be made to operate buzzer circuit by merely to connect relay 226A to the outer right armature With'this arrangegrounded battery on and contact of relay 223A.

ment, when relay 228 operates, relay 226A will operate torclose a circuit containing generator The operation of only lights the line lamp but connects grounded battery at the left armature and contact of relay 223A throughthe secondary, onright-hahd, winding of relay 221A to the sleeve of jack 211A to put a busy indication on the sleeve of jack 211. The secondary winding of relay 221A is connected in'op'position to the primary Relay 108A, in operat- I a the windingsof which are wound so as to oppose nication may now or left-hand, and helps to prevent relay 221;; from operating.

The operator at the central office answers the call by inserting answering plug 21%;! of the cord circuit selected for use, into jack 211A ofthe calling subscribers line. This energizes relay 221A as hereinafter described and thus extinguishes the lamp 212A. The operation of a key designated 196 in Fig. 3 of the drawings of the LockeKinkead application, supra, and associated with, the selected 'cord circuit, connects the operators a printer telegraph set to the loop circuit for communication with the subscribers printer at station A.

Relay22lA is caused to be operated bythe operation of a relay 134 not shown in the drawings of the present application but shown in Fig.2 'of the Locke-Kinkead application, supra. The operation of relay 221A opens the'o'perating circuit for relay 223A which releases andias statedabove, extinguishes the lamp 212A. The operation of relay 221A transfers the ring side RA of the loop circuit fromfpositive battery 224A on the inner right front contact of'relay 222A to the same positive battery, but through the right front contact of relay22la, through the right-hand, or sec-- ondary, winding of relay 219A, armature and back contact of relay 228A. The o'peration of the cord circuit repeater in establishing the connection to the central office printer telegraph set is fully described in the Locke-Kinkead application.

The operation of relay 221A removes negative battery 22)A from the loop circuit, but another battery of similar polarity is substituted in a circuit which is shown in the Locke-Kinkead application, and is. described therein as extending through resistance AA, conductor S, normally closed contact of key 196, conductor M, normally closed contact of keyi130, left-hand windings of relays 126 and 125 in series, contact and armature of relay 123, back contact and armatureof relay 139, lower inner armature and front contact and upper outer front contact and armature of relay 133 to the tip of plug 121, which corresponclsto the tip side of plug 214A of the present application, to complete a circuit over the tip side of jack 211A, contact and armature of relay 229A,'the make contact of relay221A, left-hand or primary, winding of relay 219A,'tip lead TA and back over the ring lead R. of the loop,.outer right armature and 125 front contact of relay 221A, through the righthand winding of relay 219A, armature and back contact of relay 228A to positive battery 224A. This circuit energizes-both windings of relay 219A,

each other, thereby causing the relay to release and in turn to release relay 222A.

The busy condition on the sleeve of jack 214A, formerly obtained by battery on the left-hand armature of relay 223A, is replaced upon insertion of plug 214A and upon the-release of relay 223A, by battery from thesleeve lead of the cord circuit. This battery is furnished by'the-operation of relay l34'stated' above as being shown in Fig. 2 of the'Locke-Kinkead application, supra.

,The operation of the operating key, not shown but designated 195 in the Locke-Kinkead, application, connects the central office printer telegraph set over t e answering plug 214. to the printer set at station A. Consequently, commutake place between the central' ofiice and the subscribers station A; The word operator or opr is transmitted from the central ofiice printer set and received in there- I ceiving unit '100A'of the printer setatstation A.

The subscriber then answers by operating the sender unit 101A to transmit to the central ofiice printer set the code number of the subscribers station with which a connection is desired. As soon as this information is received in the central ofiiceprinter set the opposite end, that is, calling plug 214s, of the selected cord circuit is inserted into the jack of the station desired by the subscriber at station A. Assuming that the desired station is station B, the plug 214B is inserted in jack 2113. The insertion of plug 2142, into jack 21113 of the called subscribers line causes the operation of relay 2211; because grounded battery is connected to the sleeve lead of plug 21413 as shown in the Locke-l linkead application. The tip of plug 214B completes the circuit extending through jack 21lB, contact and armature of relay 22913, left make contact of relay 2218, lefthand, or primary, winding of relay 219B, tip lead TB of the loop circuit of station E, normally closed contacts of flash key 1062, condenser 111B, bell 1043, contact No. 4 of key 105B, back contact or relay 10913, to ground at 1123. The operation of relay 2211; in the line jack circuit will complete a circuit from positive battery 22%13, back contact and armature of relay 228B, right-hand winding of relay 2193, right front contact and armature of relay 221B, ring lead RB of the loop circuit to station B, through the winding of relay 1101;, contact No. 2 of key 1053, through one winding of relay 107B, sending contacts 1013, contact No. 6 at key 105B, armature and back contact of relay 1093, to ground 1123, thereby operating relay 2193. The operation of relay 219B will operate relay 22213, which in turn will operate supervisory apparatus included in the cord circuit to inform the central office that the loop circuit to station B is completed and that ringing current may be applied to the loop to operate the ringer 10413 at station B in a manner, described in the Locke-Kinkead application, supra. The ringing current (20 cycle current) will continue to be applied to the line extending to station B until the subscriber answers. While the ringing is being applied relay 21913 in the line jack circuit will chatter, but to prevent this chattering from affecting the supervisory guard lamp (not shown but designated at 153 in Fig. 2 of the drawings of the Locke-Kinkead application) in the cord circuit, relay 22213 is designed a slow release relay which will not release when 2191; chatters. When the subscribers station B answers, as for example, by depressing the start key 1023, the relays at station B will operate in the same order as those described above in connection with station A whereat the call originated and ground will be removed from the ring side of the loop circuit; the bell circuit over the tip side of the loop circuit will be opened and leads TB andRB of the loop will be closed through the sending unit 1013 and the receiving unit 1001?, of the printer set at station E. In the line circuit the closure of the loop circuit of station B'will cause both windings of relay 21913 to become energized and relay 219B releases, because of its differential character, in a manner similar to that of relay 219A described above in connection with originating the call.

The release of relay 2193 will release relay'2221z which will remove ground from the ring side or" the cord circuit and thus cause the supervisory guard lamp in the cord circuit to be extinguished. The tip of the calling cord circuit is restored to 7 the repeater circuit and communication may now take place between subscribers through the repeater with a printer set connected in the cord circuit at the central office for monitoring the circuits.

The called subscriber may acknowledge the call in some way, as by typing his code number on the printer at station B. This code will be received on the printer sets at both stations A and the central ofiice. This connection is monitored at the central ofiice untiljsubscrioers at stations A and B are in satisfactory communication, at which time the restoring key designated 196 in Fig. 3 of the Locke-Kinkead application, supra, is operated to its normal position thereby disconnecting the printer set at the central ofiice from thethrough connection. The central ofiice printer set is now free to answer other calls.

When the call is completed a disconnect signal may be sent by either subscriber by depressing a stop key 103 which opens the locking circuit for relay 108, causing it to release and thereby open the circuit of the power supply P to the printer motor. Relai 109 will also release and the subscribers station will return to normal and restore the condition of an open tip lead and grounded ring lead. Relay 219 in the line jack circuit will now reoperate since the ring, or lefthand, winding only of the relay will be energized. Relay will now operate from the contact of relay 219 to apply ground to the ring lead of jack 211 and to the cord circuit. In the case of the calling end of the cord circuit, a supervisory lamp associated with the calling end will light. In the case of the answering end of the cord circuit a supervisory lamp circuit associated with the answering end will light.- As soon as the lighting of these lamps is noted at the central office, the cord circuit is disconnected from the jacks of the calling and the called subscribers lines, thus restoring all equipment to normal.

It should be noted that if the subscribers printer set is one of certain well known types in common use, either subscriber may send a disconnect signal to shut down, not only his own set but also that of the other station by sending two shift signals or one shift and one upper case H signal on his printer quipment. Certain mechanismlocated in the subscribers printer (not shown in the drawings since the printer forms no part of this invention) acts to open the motor control contacts. motor control contacts 113 releases relay 108 and has the same effect as opening the stop key 103.

Unattended station If the operator at the central ofiice rings a called subscriber and the subscriber does not answer, the operator may start the subscribers set and allow the calling. subscriber to send a message to the unattended station. However, before this is done, the operator will send a request to' station A asking whether or not the connection with an unattended station is desired. At this time, that is, when both the answering and the calling plugs are, in response to a call from station A'to station B, inserted in jack 211A and 211B, respectively, relays 108A and 109A at station A and relays 219A, 221A, 222A, 2191;, 2213 and 22213 at the central office are in operated positicns. Assuming that a connection to the unattended station B is desired, the operator operates key 215 in the cord circuit. Key 215, when operated, performs two functions, namely, starts the printer motor at the unattended station in a manner described in the Locke-Kinkead application, supra, and connects grounded positive The opening of the tact and right armature of relay 2221: to ground.

Relay 2283 being of the polarized type, operates in response to the positive ,currentirom battery 217 and thus applies negative battery through its front contact and armature, through the righthand winding of relay 2191;, right front contact and armature of relay 2211; to the ring side of the loop circuit of stationB, instead of the usual positive battery 22413. The reversal-of polarity on the: ring side of the loop circuit of station B operates polarized relay 1103 at station B, which in operating, closes a circuit of relay 1081s in a manner similar to that described. above for station A when the start key 102 is depressed. The operation of relay 110B puts station B in an operating' condition by starting motor MB. Relay 23013 which is normally held in a noinoperated position due to-the biasing current in its righthand winding, operates simultaneously with relay 228 and closes a circuit extending from grounded battery 231B, through the winding of relay 232B, conductor 2333,, contact andarmature of relay 230B, conductor 2345 to. ground at the back contact and left armature-of, relay 235B. Relay 232B operates and locks up in a circuit extending. through its left armature and contact,

through the contact and left armature of relay 2353 to ground. Relay 232B in operating, also closes a circuit extending from grounded battery 236B,- right-hand armature and back contact of relay 235B, contactand right-hand armature of relay 232B,through the winding of relay 237B,

terminal No. 2. of bus-bar 238B, conductor 239, continuous ring, brush and short segment of the start distributor, through the winding of relay 240, conductor 241, terminal No. 1 of bus-barv 2383, contact and 'left'outer armature of relay 2323, to ground. Relay 240, which is of the slowto-operate type, operates and closes an obvious operating circuit for releasemagnets 242 to254. The operation of the release magnet starts the brushes rotating over their respectively associated rotary distributors shown opposite the magnets. Relay 23'73 operates and subsequently ef-.

fects the operation of rotary magnet 255B; However, it is released as soon as the brush on the start distributor passes off the short segment and-causes the release of rotary magnet 25513. The release of magnet 255B causes the brushes of rotary stepper switch 256]; to simultaneously move in the same phase one rotary step along their respectively associated banks to the first operative contact on the right-hand bank. The right-hand brush in moving onto its first contact closes a circuit extending from grounded'battery 2573, through the left-hand winding of relay 229B, right-hand brush at its first operative contact of switch 256B, terminal No. 3 of bus-bar 238B, conductor 258, continuous ring, brush and segments S, l, 2,13, 4 and 5 of'the shift distributor, the segments being engaged-by the brush in the order mentioned, to ground on segments 1, 2,4 and 5. R$131Y'229B, which is normally maintained in'a non-operated position by the biasing current continuously flowing through the right-hand winding} operates in the circuit just tracedas a vibrating relay, that is, it operates when the brush passes over segmentsl, 2, 4 and 5 and releases when the brush passes over the remaining segments. relay 228 alternately opens and closes the fundaments S, 1 2, 3, 4 and 5, of thcirrespective. die- The vibratory operation of mental circuit which extends from grounded negative battery on the front contact and armature of relay 228 through the right-hand winding of relay 2193, front contact and outer right-hand armature of relay 221B, ring lead RB, through the winding of polarized relay 1l0B, contact-No.2,of key 1053, through one winding of polarized relay 107B, sending unit 1013, contact No. 6 of key 105 armature and front contact of relay 169B,-normally closed contact of key 105:5, tip lead TB, lefthandwinding of relay 219s, lower contact and left armature of relay 221B, armature and contact of relay 229B, tip spring of jack 211B, tip of plug 214B, tip of plug 214A, tip spring of jack 211A,. contact and armature of relay 229A, left armature and lower contact of relay 221A, through the left-hand winding of relay 219A, tip lead TA, normally closed contact of key 106A, front contact and 221A, through the righthand winding of relay 219A, armature and back contact of relay 2285, to 1&0 grounded positive battery 224A. The direction of current through the winding of relays 107a and 107A operatesboth relays and the alternate opening and closing of the fundamentalcircuit at the armature of relay 2293, due to impulses received fromthe. shiftidistributor in Fig. 3, will have a corresponding eifecton each of the receiving units or printer magnets 10 s and 190A. The operation of the printer magnets in response to the shift-signal causes the type bars of the printerset at each subscribers stationfto be shiftedto record figures or upper-case characters. I V

As the distributor brushes complete a'revolution and the brush of the start distributor llO again engages 1ts associated short segment the operating circuit for relay 240 is again momentarily closed to operate the release vmagnets and to allow the brushes to continue rotating. Relay 2373, the winding of which is included in the operating circuit for relay 240, also operates momentarily to step the brushes on the .banks of switch 2563 to their second contacts. As the distributor brushes continue rotating over segtributors, a combination of impulses is trans mitted corresponding to the first numerical digit of the called station number. The distributor capable of transmitting numerical signals, may be connected in any desired order to the contacts of the right-hand bank of stepper switch 2563 by means-of the cross-connecting rack com prising bus-bars 238Band 25913. There is one cross-connecting rack provided for each subscribersstation and the numerical digits corresponding to the digits of a, subscribers station number are connected by means of the contacts on the right-hand bank of the stepper switch associated with the subscribers station, The system shown herein provides for four numerical digits to a number. Therefore at the beginning of each revolution of the distributor brushes the brushes on both banks of an engaged stepper switch rotates through four steps to complete the transmission of the signal combinations con- 14-5 stituting the called station number to boththe calling and the called station where'thenumber is typed on the local printer sets. The calling subscriber is informed by these means that :the

connection established is correct. Itis understood that the scope of the invention disclosed herein is not limited to four digits in the subscribers number but that additional digits, either numerical or letters, may be employed by increasing the number of contacts on the switch banks, if necessary.

Immediately after the transmission of the signal combination for the fourth digit, the space distributor is connected to the next or sixth contact of the stepper switch and a space signal is then transmitted. The remaining contacts on the switch are connected in multiple with the sixth contact and are likewise connected to the space distributor, so that during each of the subsequent revolutions of the distributor brushes, the space signal is transmitted. When the brush on the operating bank of the stepper switch reaches the last contact, the brush on the asso ciated bank reaches its last contact, which is connected to a circuit extending from ground on the brush, through the winding of relay 23513 to grounded battery 236B. Relay 235B operates, opens the locking circuit for relay 2333, maintains open the start circuit for the distributors and the operating circuit for the stepping switch, connects ground to the operating circuit for relay 229B, whereby relay 229B operates to maintain the fundamental circuit opened and closes an operating circuit for release magnet 25013 which operates and restores both brushes to their nor mal position. The rotary stepper switches have releasing arrangements, self-interrupting in operation, and are of a type well known in the automatic telephonic art. a

As soon as the brushes on the left-hand back of stepper switch 256B moves oif the last contact, relay 235B releases thereby restoring relay 22913 to its normal position so that the fundamental circuit is now closed and ready to transmit a message from the calling station A to the called station B.

In the arrangement shown in Fig. '2 of the drawings, the stepper switch 25613 is so connected through its associated cross-connecting rack as to receive the transmitted combinations from the distributors Nos. 6, 5, 4 and 3 in the sequence mentioned. Consequently when station B is called and is unattended at the time, the number printed at the printer set of the calling station is 6543 which is the number of station B. Should the station A be called, the number printed at the printer set of the calling station would be 6654 as indicated by the cross-connection at the rack constituted of bus-bars 238A, and 259A.

The disconnection between subscribers stations is accomplished at the conclusion of a message in the manner described in the Locke- Kinkead application, supra.

It will be noted that a special impulse is put upon a called line, in this case, a reversal of polarity, to start the called subscribers motor, and that the impulse functions to cause transmission from apparatus at the central station of a signal verifying the called subscribers number. In accordance with the more generic concept of the invention this special impulse may consist of a potential or succession of potentials of different forms suitable to effect the desired result which may or may not perform other functions in the systems. Furthermore, the invention from another generic aspect may assume diiferent forms depending on the particular form of apparatus at the central exchange or of the form or nature of the link circuits connecting the subscribers.

What is claimed is:

1. A telegraph exchange system for interconnecting at a central oiiice in a plurality of subscribers lines for communication purposes, characterized in this that the equipment at the central off ce for repeating back to a calling subcribers line the code "number corresponding to a connected called subscribers line, comprises circuit means associated with each subscribers line, a plurality ofsignal transmitting devices arranged to be selected in any desired combination by any one of said circuit means, and crossconnecting means for connecting one or more of said devices with any one or" said circuit means.

2. An answer-back arrangement for a telegraph exchange system comprising a plurality of subscribers stations, a central ofiice, circuit means located at said central office, individual to each of said stations and connected to the line jack circuit of a called subscribers station for generating and transmitting back to a calling subscriber the code number corresponding to a connected called subscribers station, said circuit means being responsive to a single operation of a key for repeating back the called number of the connected called station.

3. In a telegraph exchange system, a central ofiice, subscribers stations, cord circuits at said central office for interconnecting said subscribers stations for communication purposes, switching means in each of said cord circuits, circuit means individual to each of said subscribers stations andcontrolled by any one of said switching means for answering back, when desired by a calling subscriber, the code number of the station to which a calling subscribers station-is connected.

4. A telegraph exchange system, according to claim 3, wherein the circuit means comprises a rotary stepper switch adapted to be rotated at definite intervals through its successive steps, in response to a single operation of said switching means to thereby cause to be recorded at the calling subscribers station, the code number of the station to which the calling subscriber is connected.

5. A telegraph exchange system, a central office, subscribers stations, cord circuits at said central office for interconnecting said subscribers stations for communication purposes, switching means in each of said cord circuits, selective'circuit means individual to each of said subscribers stations and controlled by any one of said switching means for answering back the code number of the station to which a calling subscribers station is connected, and a plurality of sources of information at said central oilice and common to said circuit means, each of said circuit means being automatically arranged to select said sources in various combinations for transmitting to the calling subscribers station signal combinations corresponding to the code number of a subscribers station to which the calling subscribers station is connected when one of said switching means is operated.

6. A telegraph exchange system according to claim 5, wherein the source of information is a plurality of start-stop rotary distributors adapted to operate simultaneously and continuously during the transmission to a calling subscribers station, of the code number of the station to which the calling subscribers station is connected.

7. A telegraph exchange system according to claim 5, wherein the circuit means are arranged to be restored to normal as soon as the calling subscribers station has received the code number to which the calling subscribers station is connected and wherein the source of information is adapted to be restored to normal atthe same time if all other switching means in the system are in normal position.

8. A telegraph exchange system comprising a central-office, loop circuits, at jacl: at said central oifice for terminating each. of said loops,'a plurality of subscribers telegraph stations respectively included in said loop circuits, a subscribers station called number transmitting circuits at the central oifice for each of said loop circuits, cord circuits at the central oiiice, each arranged for interconnecting any two of said loop circuits, switching means in each of said cord circuits for associating the subscribers station called number transmitting circuit of one of two interconnected stations for transmitting, when said means is operated, the called number of said one station over the loop circuits of the other station to which it is connected.

9. A telegraph exchange system comprising 7' subscribers lines and interconnecting link circuits having at the central office a source adapted to'apply to a subscribers line a special voltage to set a called subscribers receiving apparatus into operation and code signal originating means located at the central office, individual to each subscribers line and controlled by the application of said voltage to send from the central station an indication verifying to the calling subscriber the identity of the called line to which the calling subscribers line is connected.

10. In a printing telegraph system, a circuit extending between two stations, mechanism individual to each of said stations, located at a point remote from one of said stations, and responsive to a special voltage applied to said circuit at said point to send signaling impulses characteristicaily adapted to verify the identity of one of said stations to the other of said stations.

GEORGE A. LOCKE. CUTI-IBERT C. LANE; 

